Rough Draft for Review: August 21, 2001

Technical Memorandum

The Bosque Hydrology Group

Middle Rio Grande Rehabilitation Concepts

Socorro Reach: Rio Puerco Confluence to Elephant Butte

 

e-mail comments to: Paul_Tashjian@fws.gov

mail comments to: Paul Tashjian, USFWS, PO Box 1306, ABQ NM 87103

 

Introduction: The following conceptual framework for the rehabilitation of the Middle Rio Grande (MRG) is the outcome of the June 2001 Bosque Hydrology Group Meeting. The concepts presented herein focus on the reaches of the MRG between the Rio Puerco Confluence with the Rio Grande and Elephant Butte Reservoir (69 river miles).

All concepts presented herein are constructed to be implemented within current levee configuration of the MRG, and current water availability. Though not critical to their short-term success, these designs will be greatly enhanced by the re-introduction of greater sediment loads into the system, the management of sediment below the 380 Bridge, and the re-shaping of the spring run-off hydrograph.

The Reach from the Rio Puerco Confluence to Elephant Butte is complex and has distinct channel morphologies depending upon location. In order to better discuss restoration of this reach, it has been divided into 5 sub-reaches; 1) Rio Puerco: Rio Puerco to San Acacia Diversion, 2) San Acacia: San Acacia Diversion to Escondida Bridge, 3) Escondida: Escondida Bridge to river mile 85.5 (just south of 380 Bridge), 4) Bosque Del Apache: River mile 85.5 to river mile 77.5, and 5) San Marcial: river mile 77.5 to Elephant Butte Reservoir.

 

Socorro Reach (Rio Puerco confluence to Elepehant Butte Reservoir Narrows) river mile 127 to 58

Current Condition: The current condition of the MRG within the Socorro Reach is both functioning and degraded, depending upon location.

Prior to the installation of 20th century projects designed to control the river; the riverís channel was actively connected to itsí flood-plain by high discharge floods; the main channel was wide (1000'-2000') and contained an active sand bed; the channel actively eroded existing flood-plain and created newer flood-plain; the riparian vegetation on the flood-plain was of a more open structure and contained areas of grasslands.

The historical functioning of the MRG within the Socorro Reach has been degraded due to bank stabilization, levee constriction of the flood plain, the installation and operation of the Low Flow Conveyance Channel, lack of high spring run-off peak flows, sediment problems (starvation below San Acacia, excess sediment below 380 Bridge due to Elephant Butte Reservoir), and invasion by non-native riparian species. Unlike reaches north of the Rio Puerco, segments of the Rio within the Socorro Reach regularly experience over bank flooding and dynamic channel mobility. These segments exhibit riverine dynamics that mimic historic conditions. The Socorro Reach also contains segments that are more similar to non- functioning reaches north of the Rio Puerco confluence.

Trends in this reach suggest that the proportion of functioning to degraded segments will decrease with time. This degradation trend is due primarily to problems with sediment, reduction in peak spring run-off flows, armoring of banks and point bars, and establishment of non native phreatophyte forests. The current condition greatly favors non-native, water consuming, phreatophyte species. Additionally, certain segments of the Socorro Reach are experiencing a depravity of sediment, while others (south of Bosque Del Apache NWR) are experiencing excessive sedimentation problems.

 

Biologic Consequences of Current Condition

1) Poorly regenerating native riparian communities.

2) Decrease of suitable habitat for native aquatic and terrestrial species.

 

Societal Consequences of Current Condition

1) Fire

           The fire risk within the modern bosque has been greatly increased because of non native species and woody debris (dead fall) accumulation.

2) Water Consumption

            Excessive water consumption within the modern bosque due to the abundance of non native phreatophytes.

3) Flooding

            Flooding hazards have increased because of the disassociation of the channel from the former flood-plain. This disconnect has decreased the potential             for flood peaks to be attenuated by the flood- plain.

 

Desired Future Condition: The desired future condition of the Middle Rio Grande within the Socorro Reach is one where natural riverine functions are enhanced and rehabilitated. These functions will allow for a dynamic, regenerating channel and an active connection between the channel and the flood-plain. Such functioning, coupled with management of spring run-off flows out of Cochiti Reservoir, will favor native forests which, enhanced by management of the bosque, will reduce fire risks, water consumption and flood hazards.

 

Primary Restoration Concerns:

-Sediment

-paucity in San Acacia sub-reach

-excess below Highway 380 Bridge

-Exotic species

-phreatophytes

-noxious weeds

-Increased spring run-off peak flows

-Constraints: flood plain development, rail road bridge

-Rehabilitation of dynamic river processes

-Temporal and spatial mosaic of native habitats

-Flood-plain encroachment by human development

-Channel width

-maintaining a wide, active channel

-Cooperation with landowners

-Cooperation with land and water management agencies

 

 

Restoration Concerns and Concepts for the sub-reaches of the Socorro Reach

Rio Puerco sub-Reach river mile 128 to 116.2

Segments:

(a) Rio Puerco confluence to Bernardo Arroyo

(b) Bernardo Arroyo to Rio Salado Confluence

(c) Rio Salado confluence to San Acacia Dam

 

Primary Concerns:

-non native phreatophytes

-noxious weeds

 

Current Condition:

 

Restoration Concepts:

 

San Acacia sub-Reach river mile116.2 to 102

Segments:

(a) San Acacia to river mile (rm) 112 (4 miles)

-coarse gravel bed, meandering channel plan form

(b) rm 112 to rm 106

-wider channel, sand bed

 

Primary Concerns:

-diminishing sediment supply

-channel morphology shifting from braided to single thread

-median sediment size shifting from sand to gravel

-disconnected floodplain

-non native phreatophytes

-noxious weeds

 

Current Condition:

-over-bank flooding at

-private lands on east side

-incised

-meandering channel, bank erosion

-developing point bars and low terraces

-bar encroachment from rm 112 to rm 106 (?)

 

Restoration Concepts:

-similar to Santa Ana Pueblo

-lowering of flodd plain

-gradient restoration facilities

-bank lowering

-mechanical maintenance of channel width

-removal of exotics on bank

-removal of exotics on floodplain

-cooperation with landowners

 

 

Escondida sub-Reach river mile 102 to 85.5

Segments:

 

Primary Concerns:

-potential for future degradation

-bar encroachment

-bank stabilization and armoring

-loss of conveyance capacity

-arroyos from east, important for water and sediment

-non native phreatophytes

-noxious weeds

 

Current Condition:

-overbank flooding at

-wide active sections vs. narrow degraded sections (1997 photo survey details)

-river mile 102- rm 101.5, narrow

-rm 101.5 to rm 100, wide

-rm 100 to rm 98, narrow

-rm 98 to rm 95, wide

-rm 95 to rm 93, narrow

-rm 93 to rm 89, wide

-rm 89 to rm 85.5, narrow

-arroyos

-(need to identify and classify as to condition)

 

Restoration Concepts:

-mechanical maintenance of channel width

-removal of exotics on bank

-removal of exotics on floodplain

-avulsions

-secondary channels

-arroyo mouth maintenance

-fire breaks around older native riparian stands

-cooperation with landowners

 

 

Bosque Del Apache sub-Reach river mile 85.5 to 77.5

Primary Concerns:

-river bed aggradation (sediment management)

-exotic species establishment (phreatophytes and noxious weeds)

-loss of valley drainage

-bar encroachment and stabilization

-channel narrowing

 

Current Condition:

-wide, active channel

-over bank flooding at 2700 cfs

-arroyos

-(need to identify and classify as to condition)

Restoration Concepts:

-enhance regeneration of native riparian species

-avulsions

-maintaining wide channel

-management of sediment transport

 

San Marcial sub-Reach river mile 77.5 to 58

Primary Concerns:

-narrow channel

-stable banks

 

Current Condition:

-over-bank flooding at

-very narrow channel width

-arroyos

-(need to identify and classify as to condition)

 

Restoration Concepts:

-opening of flood plain below San Marcial Railroad Bridge

-artificial avulsions

 

Rehabilitation Conceptual Designs Toolbox for Socorro Reach:

The following restoration concepts are in alphabetical order and do not have any importance weight placed on them.

Artificial Avulsion

Mimicry of avulsions through clearing of channel path in flood-plain and mechanical direction of active channel into desired new channel.

Bar maintenance

Maintenance if bar mobility through clearing of vegetation. This is especially important during low spring-run off years.

Bank Destabilization

Destabilize banks of the river in conjuction with bank lowering. Remove non native vegetation and associated root structures along the bank.

Bank Lowering

Using the Albuquerque Over-bank Project as a successful test, implement bank lowering at a rate of 500 acres per year for the next 20 (?) years. Return sediment removed from banks into the river.

Channels in Terrace

Cut channels within the terrace to promote a better connection between the channel and the flood-plain. These channels can be cut at different levels to allow for varying connectivity (ie, some could wet at 5000 cfs, some 2000 cfs and others at base flow. This will promote the natural recruitment of native vegetation.

Channel width maintenance

Maintenance of channel width through mechanical removal of non native vegetation on channel banks, bar control, and plowing of bank sediment into the Rio.

Collaborative Restoration Program with private landowners (including conservation easments)

Exotic Species Management

Grade Control Facility

Place Grade Control Facilities (as done at Santa Ana Pueblo) at key locations to promote upstream overbanking and dissuade further incision of the channel.

Grazing Management

Increase Spring Discharge

Increase the spring discharge peak from Cochiti Reservoir. This will promote a greater connectivity between the main channel and the flood-plain.

Native Plant Species Establishment

Secondary channels

Carving of secondary channels into the flood-plain. These channels would be active during various high flow targets.

Sediment Sources

Seek out sources of sediment to be returned to the system. Possible sources include

Sediment storage in floodplain

Understory Exotic Removal

Remove exotic understory from the bosque. Remove dead fall and litter. This will reduce water consumption, reduce fire potential, improve flood-plain ability to attenuate large floods, and improve forest health.

Woody Debris in River

Place woody debris from thinned bosques into the river. This will allow for greater braiding and return organic materials to the modern channel.